Field
The disclosed technology relates to laser devices, and more particularly to large aperture uniform-amplification laser modules.
Description of the Related Technology
The chemical formula of polycrystalline aluminium-yttrium garnet (YAG) is Y3Al5O12, or 3Y2O3.5Al2O3, where Y2O3 is 57.06 wt %, Al2O3 is 42.94 wt %. YAG is a laser host with an excellent combination of optical, mechanical and thermal properties. In laser devices with low and medium power, the quantity of yttrium aluminium garnet crystal (Nd:YAG) made of yttrium aluminium garnet far exceeds that of other laser material. Yttrium aluminium garnet crystals are prepared by melting and crystallizing certain proportions of Al2O2, Y2O2 and Nd2O3 in a single crystal furnace. The process of growing yttrium aluminium garnet crystals may include growing a crystal blank using the Czochralski method (CZ method). The thermal properties of yttrium aluminium garnet crystal make it a very suitable laser material.
The quality of crystals grown using the Czochralski method are adversely impacted by melt flow effects, transmitted vibrations, and temperature fluctuations. Due to characteristics of the crystal itself, the doping concentration of two ends of the crystal gradually rises as growth length increases. Usual methods for making a crystal bar process along the growth direction of the crystal blank, and the length of the crystal bar determines the difference of doping concentration on the crystal bar. For example, crystal bars with a diameter greater than or equal to 8 mm and a length greater than or equal to 100 mm have a difference of doping concentration of 20%-30%.
Commonly used laser amplification modules include a pump block composed of a bar, a cooling heat sink and a cooling pipe. A plate-like pump bar structure is composed of a plurality of connected pump blocks, and a plurality of plate-like pump bar structures arranged around a crystal bar in the laser amplification module. The distance from the bar on each pump bar structure to the crystal bar is the same and fixed, and the doping concentration is proportional to an absorption coefficient of the crystal bar to pump light. For a longer crystal bar with a larger diameter, the doping concentration gradient of the crystal bar on its main body may be too high, and the absorption coefficient of two ends of the crystal bar may be significantly different from that of the middle part, which makes the whole pump on the crystal bar nonuniform resulting in nonuniformity of the final gain output. Therefore, there is a need for large aperture laser modules with uniform amplification.